Zeolite beta is a well known molecular sieve catalyst which has been employed in hydrocarbon conversion processes such as dewaxing and the catalytic cracking of relatively heavy high molecular weight hydrocarbon oils. Zeolite beta, as employed in such conversion practices, was first disclosed in U.S. Pat. No. 3,308,069 to Wadlinger et al and later in a so-called improved form in U.S. Pat. No. 4,642,226 to Calvert et al. As disclosed in the patent to Calvert, among the conversation processes in which zeolite beta is particularly useful are dewaxing, hydroisomerization, cracking, hydrocracking, and aromatization through the conversion of light aliphatic hydrocarbons to aromatic hydrocarbons. As disclosed in Calvert, the zeolite beta employed in such conversion processes can be prepared by synthesis procedures involving the hydrothermal digestation of reaction mixtures, including silica, alumina, various other optional metal oxides or hydroxides, and an organic templating agent which is employed to produce the desired crystalline structure. The amount of silica and alumina in the reaction mixture may vary with a silica to alumina mole ratio in the range of 20-250, resulting ultimately in silica/alumina mole ratios of the crystalline product, ranging from less than 20 to about 60 to as high as, in one example given in Calvert, 171.
Molecular sieve catalyst, such as zeolite beta as well as numerous other molecular sieves, are commonly employed in combination with a matrix material which acts as a binder for the molecular sieve. For example, the aforementioned patent to Wadlinger discloses that the zeolite beta can be employed alone or as a dispersed mixture in combination with a low activity and/or catalytically active material which serves as a binder for the zeolite catalyst constituent. The aforementioned patent to Calvert discloses the use of inorganic materials such as clay, silica, or alumina or various composite materials such as silica/alumina, silica/magnesia, and various other binary and trinary compositions.
In addition to the use of zeolite beta in hydrocarbon conversion processes, including, for example, dewaxing, hydrocracking, or aliphatic aromatic conversation as described above, zeolite beta, as well as numerous other molecular sieves, has also been employed as a catalyst in the alkylation of an aromatic substrate. Such alkylation conversion reactions include the alkylation of aromatic substrates such as benzene to produce alkyl aromatics such as ethylbenzene, ethyltoluene, cumene or higher aromatics and the transalkylation of polyalkyl benzenes to monoalkyl benzenes. Typically, an alkylation reactor which produces a mixture of mono- and poly-alkyl benzenes may be coupled through various separation stages to a downstream transalkylation reactor. Such alkylation and transalkylation reactions can be carried out in the liquid phase, in the vapor phase or under conditions in which both liquid and vapor phases are present.
U.S. Pat. No. 4,185,040 to Ward et al discloses an alkylation process employing a molecular sieve catalyst of low sodium content, less than 0.5 wt. % Na2O, which is said to be especially useful in the production of ethylbenzene from benzene and ethylene and cumene from benzene and propylene. Examples of suitable zeolites include molecular sieves of the X, Y, L, B, ZSM-5, and omega crystal types, with steam stabilized hydrogen Y zeolite being preferred. Specifically disclosed is a steam stabilized ammonium Y zeolite containing about 0.2% Na2O. Various catalyst shapes are disclosed in the Ward et al patent. While cylindrical extrudates may be employed, a particularly preferred catalyst shape is a so-called “trilobal” shape which is configured somewhat in the nature of a three leaf clover. The surface area/volume ratio of the extrudate should be within the range of 85-160 in.−1. The alkylation process may be carried out with either upward or downward flow, the latter being preferred, and preferably under temperature and pressure conditions so that at least some liquid phase is present, at least until substantially all of the olefin alkylating agent is consumed. The Ward et al patent states that rapid catalyst deactivation occurs under most alkylating conditions when no liquid phase is present. In the Ward process, as well as in the various conversion processes described previously, the zeolite may be incorporated with a porous mineral oxide binder to arrive at the particulate catalyst configuration such as the trilobal configuration. Thus, Ward discloses the use of alumina gel, silica gel, silica/alumina co-gels, various clays, titania, and other mineral oxides with alumina being preferred for use in combination with the preferred zeolite-Y.
As is the case with zeolite employed in conversion processes or in alkylation processes, procedures involving zeolite beta for alkylation or transalkylation processes are normally carried out employing alumina as a binder providing a matrix for the zeolite catalyst. Thus, U.S. Pat. No. 4,891,458 to Ennes et al discloses a process for the liquid phase alkylation or transalkylation of an aromatic hydrocarbon employing a zeolite beta catalyst. The zeolite beta is disclosed in Ennes et al to have a silicon to aluminum atomic ratio of greater than 5:1 and less than 100:1 and preferably greater than 5:1 and less than 50:1. Ennes discloses alkylation under conditions in which the mole ratio of aromatics to olefins is at least 4 to 1 in order to prevent rapid catalyst fouling. The reaction temperature ranges from about 100° to 600° F. and the reaction pressure is typically about 50-100 psig and sufficient to maintain at least a partial liquid phase. Preferably the zeolite beta used in the Ennes procedure is predominantly in the hydrogen form, arrived at by ammonium exchange of the synthesized product followed by calcination. Innes discloses that the pure zeolite may be employed with an inorganic oxide binder, such as alumina, silica, silica/alumina, or naturally-occurring clays. Innes continues that the preferred inorganic binder is alumina.
Another alkylation procedure is disclosed in U.S. Pat. No. 4,798,816 to Ratcliffe et al and involves the use of molecular sieve alkylation catalysts which have been treated in a manner to improve selectivity to monoalkylation, specifically in the propylation of benzene to produce cumene. Selectivity is increased by at least one percentage point by first depositing a carbonaceous material on the catalyst and then subjecting the resultant carbon containing catalyst particles to combustion. Specific zeolitic crystalline molecular sieves include those selected from the group of Y zeolites, fluorided Y zeolites, X zeolites, zeolite beta, zeolite L, and zeolite omega. The preferred Y-type zeolites may be dealuminated to produce an overall silica to alumina ratio above 6. As is the case in the previous references, the preferred inorganic refractory oxide material used as a binder is alumina, specifically catapal, although other binders such as alumina, gallia, thallia, titania, zirconia, beryllia, silica, silica-alumina, and various other materials are disclosed.
EPA publication 467,007 to Butler discloses other processes having separate alkylation and transalkylation zones employing various molecular sieve catalysts and with the output from the transalkylation reactor being recycled to an intermediate separation zone. Here, a benzene separation zone, from which an ethylbenzene/polyethylbenzene fraction is recovered from the bottom with recycling of the overhead benzene fraction to the alkylation reactor, is preceded by a prefractionation zone. The prefractionation zone produces an overhead benzene fraction which is recycled along with the overheads from the benzene column and a bottom fraction which comprises benzene, ethylbenzene and polyethylbenzene. Two subsequent separation zones are interposed between the benzene separation zone and the transalkylation reactor to provide for recovery of ethylbenzene as the process product and a heavier residue fraction. The polyethylbenzene fraction from the last separation zone is applied to the transalkylation reactor and the output there is applied directly to the second benzene separation column or indirectly through a separator and then to the second benzene separation column. Butler discloses that the alkylation reactor may be operated in the liquid phase with a catalyst such as zeolite-beta, zeolite-Y or zeolite-omega or in the vapor phase, employing a catalyst such as silicalite or ZSM-5.
Another procedure involving the liquid phase alkylation of an aromatic substrate is disclosed in EPA Publication No. 507,761 to Shamshoum et al. This procedure involves the use of a molecular sieve catalyst which is based upon zeolite beta but which has been modified by the incorporation of lanthanum. The lanthanum-modified zeolite beta catalyst is disclosed in Shamshoum et al to provide little or no xylene make under the mild liquid phase alkylation conditions as contrasted with the use of zeolite beta in the hydrogen form. In the Shamshoum et al procedure, the initial zeolite beta preferably has a silica/alumina ratio of between 20 to 50, which is initially subject to an ion exchange step followed by calcination at a temperature of about 570° C. for 2 or more hours. After subsequent ion exchange and calcination procedures, the molecular sieve is dried followed by incorporation of lanthanum into the zeolite system by ion exchange with a lanthanum salt solution. Shamshoum et al disclosed that the lanthanum beta zeolite is mixed with a binder, such as alumina sol, gamma alumina, or other refractory oxides, to produce a zeolite binder mixture which is then pelletized.
Other procedures involving liquid phase alkylation of benzene are disclosed in U.S. Pat. Nos. 5,030,786 to Shamshoum et al, and 5,073,653 to Butler. Shamshoum '786 discloses the use of molecular sieves having a pore size greater than 6.5 angstroms, specifically zeolites Y and beta having a pore size within the range of 7-7.5 angstroms. The patent to Butler discloses alkylation of benzene in the liquid phase employing catalysts including zeolites, such as zeolite omega, zeolite beta, and zeolite Y. Butler discloses that the operation of the alkylation reactors under relatively mild liquid phase conditions enables the use of relatively low benzene-ethylene mole ratios over the reactor of about 5:1 or less and preferably 4:1 or less down to about 2:1. Higher ratios up to 15:1 are also disclosed. Butler specifically discloses a catalyst containing 80% crystalline zeolite omega and 20 wt. % alumina binder.